In order to protect data from disasters and other events, data is often backed up to a remote location by remote copying. Remote copying modes include a synchronous mode and an asynchronous mode. In the asynchronous mode, remote copying of data to the copy destination storage apparatus is performed asynchronously with updating of data in the copy source storage apparatus. Further, the asynchronous remote copying mode includes a remote copying mode that does not guarantee the data update sequence and a remote copying mode (sequence-guaranteed remote copying mode) that guarantees the data update sequence.
In the sequence-guaranteed remote copying mode, the copy source storage apparatus uses part of the cache memory of each of controllers thereof as a buffer, and stores Input/Outputs (I/Os) to a copy session in the buffer. Then, the copy source storage apparatus copies data stored in the buffers by the respective controllers of the copy source storage apparatus to the copy destination storage apparatus collectively, that is, in units of buffer sets.
Thus, the copy source storage apparatus is able to copy data to a standby volume (copy destination storage apparatus) located in a remote location, while guaranteeing the data update sequence in accordance with Write I/Os from the host to an operation volume (copy source storage apparatus). Further, since data is transferred via buffers, the copy source storage apparatus may use a low-bandwidth network for the data update capacity.
See, for example, Japanese Laid-open Patent Publications No. 2011-158948 and No. 2005-222274.
Recent storage apparatuses tend to have an increased number of disks so as to provide greater data capacity. Further, such storage apparatuses tend to have an increased number of controllers so as to process a large amount of data. Since each controller includes a buffer used for sequence-guaranteed remote copying, the number of buffers used for sequence-guaranteed remote copying is also increased.
However, in order to guarantee the sequence of remote copying, the copy source storage apparatus transfers data in units of buffer sets when the filling rate of any of buffers exceeds a threshold. That is, an increase in the number of buffers causes a variation in data filling rate between buffers, which results in a reduction in data filling rate on a per buffer set basis.